This invention relates to improvements in small diameter low profile dilatation catheters used in angioplasty and particularly coronary angioplasty. More particularly, the invention concerns the type of dilatation catheter which incorporates a wire-like shaft that is sufficiently torsionally rigid so as to be steerable thereby enabling the catheter to be selectively guided and steered to the desired location in the patient's coronary arteries.
In performing coronary angioplasty, it often occurs that the physician may wish to use a catheter different than the one originally inserted into the patient. For example, this may occur if the initial selection of catheter balloon size was inappropriate to treat the patient's stenosis or some other event occurs that would make use of a different catheter desirable When the catheter is of the type that uses a separate movable guidewire, the catheter may be exchanged in a well known procedure in which an exchange wire is substituted for the movable guidewire (or the length of the guidewire is extended with an extension wire): then the catheter is withdrawn over the exchange wire and the replacement catheter is threaded over the exchange wire and is thereby guided to the stenosis. By maintaining the guidewire in position during the exchange procedure, the replacement catheter is easily and quickly advanced to the stenosis.
The foregoing catheter exchange procedure has not been usable with small diameter low profile dilatation catheters of the type that incorporate an integral guidewire because the balloon catheter cannot be separated from the guidewire. Thus, when it is desired to exchange one such dilatation catheter for another, the typical procedure is to withdraw the entire catheter and integral guidewire and then replace it with the desired catheter. Withdrawal of the catheter, however, results in loss of position of the catheter in the stenosis. As a result, the next placed catheter must be re-manipulated through the patient's arterial system to position the balloon in the stenosis. The replacement of the catheter typically involves time consuming manipulation and steering to guide the catheter to place its balloon within the stenosis. The additional procedure increases somewhat the risk of trauma to the patient.
A similar problem is presented when it is desired to exchange a conventional movable guidewire dilatation catheter for a catheter of the type having an integral guidewire. Again, in order to make such an exchange, it has been necessary to remove completely the movable guidewire and the dilatation catheter to permit insertion of the integral guidewire type of catheter. Because there is nothing to guide the catheter directly to the stenosis, it is necessary for the physician to go through all the manipulations necessary to steer and guide the new catheter to the stenosis.
It would be desirable, therefore, to provide a system by which catheter exchanges involving small diameter low profile dilatation catheters having an integral guidewire could be effected easily, quickly, without loss of position and with minimal trauma. It is among the objects of the invention to provide such a system.